1. Technical Field
This invention pertains generally to angiography, and more particularly to 3D magnetic resonance imaging angiography.
2. Background Discussion
Contrast-enhanced magnetic resonance angiography (CE-MRA) is particularly appealing for evaluating patients with cardiovascular disorders due to concerns associated with alternative imaging modalities, including repeated exposure to ionizing radiation, invasive catheterization and the use of iodinated contrast agents. Detailed delineation of the vascular anatomy provided by CE-MRA is important for planning surgical or catheter interventions.
Conventional breath-hold first-pass CE-MRA provides diagnostic visualization of the majority of extra-cardiac vessels. However, first-pass CEMRA is generally applied without cardiac gating and provides limited or poor definition of intra-cardiac anatomy, e.g. ventricular outflow tracts, cardiac chambers and coronary anatomy, such that supplemental 2-D cardiac cine MRI is usually required. Cardiac gated 3D CEMRA has been described previously, but the requirement to image the first pass of a contrast bolus in a breath-hold has imposed restrictions on temporal resolution, spatial resolution and anatomic coverage, relative to their non-gated counterparts.
Furthermore, patients younger than 6 years old are generally unable to cooperate with breath-hold instructions. Therefore, in several institutions, general anesthesia and mechanical ventilation are preferred in these young patients where a controlled breath-hold is achieved by temporarily pausing the MR-compatible ventilator. Breath holding is repeated for several temporal phases of contrast enhancement and also for multiple, individual cardiac cine acquisitions. For the vast majority of patients, controlled apnea is a very safe procedure when carried out by specialist anesthesiologists or neonatal intensive care unit (NICU) staff. Nonetheless, in sick infants and neonates with complex congenital heart disease (CHD), it is desirable to minimize the frequency and duration of breath holding, while at the same time providing sufficiently detailed anatomic and functional evaluation of the heart and great vessels to guide patient management.
Moreover, in infants and patients with severe renal impairment, concerns about nephrogenic systemic fibrosis (NSF) and warnings from the Food and Drug Administration (FDA) have caused referring physicians to shy away from the use of GBCAs.
CE-MRA is typically performed within a breath-hold of 20-25 seconds during first pass of a gadolinium based contrast agent (GBCA). Due to the limitation in breath-hold time and first-pass of the contrast agent, these acquisitions are generally not gated to cardiac ECG signal and those that are gated sample only a single phase of the cardiac cycle. As a result, the conventional CE-MRA falls short in providing detailed definition of intra-cardiac anatomy, such as the cardiac chambers, the coronary blood vessels, the valves, etc. This is particularly limiting for children with congenital heart diseases, where high resolution imaging of anatomy and function is crucial.
For example, patients younger than 6 years old are generally unable to cooperate with breath-hold instructions. Therefore, general anesthesia and mechanical ventilation are preferred in these young patients where a controlled breath-hold is achieved by temporarily pausing the MR-compatible ventilator. Breath holding is repeated for several temporal phases of contrast enhancement and also for multiple, individual cardiac cine acquisitions. For the majority of patients, controlled apnea is a safe procedure when carried out by specialist anesthesiologists or neonatal intensive care unit (NICU) staff. Nonetheless, in sick infants and neonates with complex congenital heart disease (CHD), it is desirable to minimize the frequency and duration of breath holding, while at the same time providing sufficiently detailed anatomic and functional evaluation of the heart and great vessels to guide patient management.